Blender 2.77 cycles. Smoke generation stops working when I click on flow
For smoke to work you need at least two things:

A Smoke Flow Object, the source where the smoke is generated from.

A Smoke Domain that contains the smoke simulation.

When you select an object and apply Quick smoke, a new object appears. That "newly created object" is the smoke domain.

If you convert the smoke domain to flow, the smoke simulation will not work. To change the flow settings select the original object.